Piezoelectric Actuation Mechanism Involving Extrinsic Nanodomain Dynamics in Lead‐Free Piezoelectrics

Piezoelectric materials play a key role in applications, while there are physically open questions. The physical origin of piezoelectricity is understood as the sum of contributions from intrinsic effects on lattice dynamics and those from extrinsic effects on ferroic‐domain dynamics, but there is an incomplete understanding that all but intrinsic effects are classified as extrinsic effects. Therefore, the accurate classification of extrinsic effects is important for understanding the physical origin of piezoelectricity. In this work, high‐energy synchrotron radiation X‐ray diffraction is utilized to measure the response of BiFeO3−BaTiO3 piezoelectrics and the intrinsic/extrinsic contribution to electric fields. It is found from crystal structure and intrinsic/extrinsic contribution, using the analysis involving structure refinement with various structural model and micromechanics‐based calculations, that Bi3+‐ion disordering is important for realization of piezoelectricity and nanodomains. Here, an extrinsic effect on the rearrangement of nanodomains is suggested. The nanodomains, which are formed by the locally distorted structure around the A‐site by Bi‐ion disordering, can significantly deform the material in the BiFeO3−BaTiO3 system, which contributes to the piezoelectric actuation mechanism apart from the extrinsic effect on ferroic‐domain dynamics. Bi‐ion disordering plays an important role in realizing piezoelectricity and nanodomains and can provide essential material design clues to develop next‐generation Bi‐based lead‐free piezoelectric ceramics. The piezoelectric actuation mechanism in pseudocubic structures is clarified by the calculation of extrinsic/intrinsic contribution. Although only intrinsic contributes to the piezoelectricity, it does not match the piezoelectricity of BiFeO3–BaTiO3. It is clarified that extrinsic effect on nanodomain rearrangements is revealed in BiFeO3–BaTiO3. Extrinsic effect on nanodomain rearrangement is involved in the actuation mechanism of piezoelectricity.